1 00:00:01,110 --> 00:00:03,230 Let's not look at a very important topic. 2 00:00:03,420 --> 00:00:10,790 Access levels not really understand what packages are what classes are and also what members construct 3 00:00:10,790 --> 00:00:13,730 ridiculous like reliables methods and so on. 4 00:00:14,210 --> 00:00:20,090 But our main goal is to build very design software and for that there are certain design principles 5 00:00:20,960 --> 00:00:26,840 in the next lesson they will learn about one such design principal information hiding because a name 6 00:00:26,840 --> 00:00:30,270 suggests has something to do with hiding off information. 7 00:00:31,250 --> 00:00:35,470 For example women not want our variables to be accessed directly. 8 00:00:35,840 --> 00:00:38,540 That is we want to hide our variables. 9 00:00:38,540 --> 00:00:44,330 For instance if you recall our student example we were accessing the name variable in the Student class 10 00:00:44,420 --> 00:00:45,570 directly. 11 00:00:45,890 --> 00:00:51,810 And that is a bad practice as we will see when learning about information hiding So you talking about 12 00:00:51,810 --> 00:00:58,200 restricting access to some of the stuff like Redeemer's information hiding is about how to provide such 13 00:00:58,200 --> 00:01:00,980 restrictions on to achieve it. 14 00:01:00,990 --> 00:01:06,680 It uses the concepts that we learn in this lesson so let's go ahead and learn about access elements 15 00:01:08,880 --> 00:01:14,860 access limits basically help in providing restrictions on accessing classes on their members. 16 00:01:16,570 --> 00:01:22,390 For example when it comes to classes V.M. want a class to be accessible only to classes within the same 17 00:01:22,390 --> 00:01:23,620 package. 18 00:01:23,620 --> 00:01:29,440 That is we don't want our class to be accessible outside of it's package for example we may not want 19 00:01:29,440 --> 00:01:34,130 classes outside the package to create an instance of one particular class. 20 00:01:34,600 --> 00:01:39,550 That is we want the class to be instantiated only by classes in the same package. 21 00:01:39,550 --> 00:01:47,430 So that's a kind of restriction however in most cases you would want the class to be accessible to every 22 00:01:47,430 --> 00:01:48,600 other class. 23 00:01:48,600 --> 00:01:52,830 There is two classes in the same package as well as two classes outside of each package. 24 00:01:54,190 --> 00:02:00,910 And for this to happen you will include a key word called public in the class declaration and here is 25 00:02:00,910 --> 00:02:07,570 how it would be when used in the class declaration for basics to modeless hit public is referred to 26 00:02:07,570 --> 00:02:14,650 as an access modifier and it should come before the key word us now if you place it in between what 27 00:02:14,650 --> 00:02:17,870 class and the class name then you get a compiler error. 28 00:02:18,690 --> 00:02:20,700 In fact you cannot have anything in between. 29 00:02:20,710 --> 00:02:25,480 The key word class name so you use public modifier. 30 00:02:25,530 --> 00:02:28,420 If the accessibility of the class is public. 31 00:02:28,670 --> 00:02:32,510 But for the previous kids their accessibility is only within the package. 32 00:02:32,540 --> 00:02:36,700 We do not use any modifier So that's not the focus. 33 00:02:36,740 --> 00:02:41,330 So if you don't use any access modifier then it implies that the class is accessible only within the 34 00:02:41,330 --> 00:02:42,040 package. 35 00:02:43,060 --> 00:02:50,260 Also you know the title is accessibility for book classes as well as interfaces interfaces and important 36 00:02:50,260 --> 00:02:54,600 concepts like class and will be introduced when discussing object oriented concepts. 37 00:02:56,470 --> 00:03:01,620 Similitude there are certain restrictions when it comes to members of a class like reliables methods 38 00:03:01,660 --> 00:03:07,140 constrictors or even member classes or member interfaces which will be introduced later. 39 00:03:07,450 --> 00:03:14,200 Let's see what these distinctions are are one restriction is for a member of that class to be accessible 40 00:03:14,320 --> 00:03:19,630 only within the class in which it is defined that is outside of the class that members should not be 41 00:03:19,630 --> 00:03:20,390 accessible. 42 00:03:21,290 --> 00:03:26,720 For example you may want a variable to be accessible only within that class like an arts methods are 43 00:03:26,720 --> 00:03:30,280 constructors but not to any code outside of the class. 44 00:03:31,710 --> 00:03:36,480 This you would use an access modifier call when declaring the variable. 45 00:03:36,520 --> 00:03:38,840 It's not just that the member is private but across 46 00:03:41,380 --> 00:03:46,690 sometimes you may want a particular member to be accessible not only with the next class but also to 47 00:03:46,720 --> 00:03:49,130 other classes in the same package. 48 00:03:49,210 --> 00:03:55,270 For this we do not use any access Madhi where sometimes this access level is also referred to as package 49 00:03:55,270 --> 00:03:58,400 private as the accesses private with a package. 50 00:04:00,380 --> 00:04:06,010 We may also want a member to be accessible to all classes in the same package like in the previous case 51 00:04:06,020 --> 00:04:06,240 . 52 00:04:06,500 --> 00:04:12,570 But in any Sheean we may want that member to be accessible to all subclasses of its costs on those up 53 00:04:12,570 --> 00:04:18,560 classes maybe outside the package do some classes are not discussed and they will be introduced to encumbering 54 00:04:18,620 --> 00:04:21,590 inheritance which is an object oriented concept. 55 00:04:22,440 --> 00:04:23,110 So let's start with you. 56 00:04:23,110 --> 00:04:26,840 What's the process for now but not at this access level. 57 00:04:26,880 --> 00:04:35,060 You would have to use an access modifier called protected when declaring the variable finally be me 58 00:04:35,060 --> 00:04:40,520 I also want certain members of the class to be accessible to any court regardless of where the court 59 00:04:40,520 --> 00:04:41,420 is. 60 00:04:41,480 --> 00:04:45,510 There is a court maybe inside the package or outside the package too. 61 00:04:45,620 --> 00:04:50,990 So that's the public access level and you would use an access modifier called public when declaring 62 00:04:51,000 --> 00:04:58,310 that even know that anything declared with public Marty for being a class or interface or any of their 63 00:04:58,310 --> 00:05:05,720 members that particular member would become part of the API as any code outside the package can also 64 00:05:05,720 --> 00:05:06,500 access it. 65 00:05:07,570 --> 00:05:12,170 Just know that these access levels are ordered from most to least restrictive. 66 00:05:12,850 --> 00:05:19,030 So first one is most strict so as visibility of class member is only within that class. 67 00:05:19,030 --> 00:05:25,580 Similarly last one is at least a strip built as a class member is accessible to any quarter ourself 68 00:05:25,620 --> 00:05:32,670 all the money for our private and public are to use most of the time it is used relatively rarely and 69 00:05:32,940 --> 00:05:41,180 default package by what access is also commonly used but maybe not as much as private and public finally 70 00:05:41,180 --> 00:05:46,130 know that interface's also have members like we deal with some matters but it's not really about their 71 00:05:46,130 --> 00:05:47,840 accessibility for now. 72 00:05:47,980 --> 00:05:53,990 We will discuss when we get to interface's So as you can see when compared to classes and interfaces 73 00:05:54,260 --> 00:06:00,410 members of a class have two additional access level restrictions that is private unprotected restrictions 74 00:06:01,400 --> 00:06:06,190 public and default access levels apply to both classes as well as their members. 75 00:06:07,340 --> 00:06:12,310 Let's let's just discuss a little bit more about only private modifier as there is one point I would 76 00:06:12,310 --> 00:06:14,830 like to highlight regarding private modifier. 77 00:06:16,550 --> 00:06:20,660 Let's see hope private modifier is used with various methods. 78 00:06:20,980 --> 00:06:22,970 The same applies to other modifiers too. 79 00:06:23,170 --> 00:06:25,350 So you don't have to look at them explicitly. 80 00:06:26,940 --> 00:06:31,050 If you're declaring a variable that's private you would use a modifier private. 81 00:06:31,380 --> 00:06:37,580 So not this variable would be visible only with the next class also the private variables can be defined 82 00:06:37,580 --> 00:06:44,190 at class level on me or not matters live in any variable defined in a method that is a local variable 83 00:06:44,360 --> 00:06:50,210 is already private to the ometer so using public modified with a local variable will give you a compiler 84 00:06:52,120 --> 00:06:54,670 Similarly you can find a method as a pirate. 85 00:06:55,300 --> 00:07:00,640 Not that he had to modify a pirate cannot be specified in between the methods returned by the method 86 00:07:00,640 --> 00:07:01,330 name. 87 00:07:01,600 --> 00:07:06,620 It has to be specified before it might otherwise be get a compiler. 88 00:07:06,730 --> 00:07:09,170 You just cannot have anything in between the mattress. 89 00:07:09,180 --> 00:07:17,680 You can type on them that's name next is the point I wanted to highlight using private modifier implies 90 00:07:17,690 --> 00:07:18,190 that it is. 91 00:07:18,290 --> 00:07:23,190 But I work with a class not by weight to objects of its class. 92 00:07:23,210 --> 00:07:24,450 Let's look at an example. 93 00:07:26,560 --> 00:07:29,590 This is a stripped down version of our student class example. 94 00:07:29,740 --> 00:07:36,130 Here we have a student class variable ID declare that's private and disgress has two objects reference 95 00:07:36,130 --> 00:07:37,870 by variables S1 and S2. 96 00:07:38,660 --> 00:07:41,210 There is also the class course with its own object. 97 00:07:42,920 --> 00:07:50,200 Not you can see object Essman can access I'll be full of objects as to even though ideas by to s2. 98 00:07:50,720 --> 00:07:55,020 That's because objects of a class can access each other's private stuff. 99 00:07:57,060 --> 00:08:03,670 Hoher the class course or even its object cannot access the ID field of either student class or any 100 00:08:03,670 --> 00:08:04,810 of its objects. 101 00:08:05,700 --> 00:08:11,460 So once again if something is declared private It means it is private goods class or not but the objects 102 00:08:11,460 --> 00:08:18,400 of its class you may also recall that when introducing packages it was mentioned that one use of package 103 00:08:18,400 --> 00:08:26,240 is security so that you can see here by using access modifiers like private we restrict what parts of 104 00:08:26,240 --> 00:08:29,180 the code can be seen outside the class. 105 00:08:29,420 --> 00:08:31,540 And of course outside the package too. 106 00:08:32,180 --> 00:08:35,240 So that's the whole discussion on access modifiers. 107 00:08:35,510 --> 00:08:40,490 Our next as we mentioned earlier they will look at an important design principle called information 108 00:08:40,490 --> 00:08:46,970 hiding which is a tool by using access modifiers we would also look at a couple of important effective 109 00:08:47,180 --> 00:08:54,060 items in understanding information hiding post offical wedding information hiding he had them all with 110 00:08:54,060 --> 00:09:00,120 the student example that we talked earlier will be enhanced the enhancement will be based on what we 111 00:09:00,120 --> 00:09:05,130 learn and information hiding there we will be using access modifiers. 112 00:09:05,250 --> 00:09:08,060 And so you will see them in action in that demo. 113 00:09:08,380 --> 00:09:08,960 Thank you.